<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>超时与网络异常</title>
</head>
<style>
    #result {
        width: 200px;
        height: 100px;
        border: solid 1px #903;
    }
</style>

<body>
    <button>点击发送请求</button>
    <div id="result"></div>
    <script>
        const btn = document.getElementsByTagName('button')[0];
        const result = document.getElementById('result');
        btn.addEventListener('click', function() {
            const xhr = new XMLHttpRequest();
            // 超时设置
            xhr.timeout = 2000;
            // 超时回调
            xhr.ontimeout = function() {
                    alert('网络异常，稍后重试');
                }
                // 网络异常的回调
            xhr.onerror = function() {
                alert('你的网络似乎出了一些问题');
            }
            xhr.open('GET', 'http://127.0.0.1:8000/delay');
            xhr.send();
            xhr.onreadystatechange = function() {
                result.innerHTML = xhr.response;
            }
        })
    </script>
</body>

</html>